title: Transition from transparent aerogels to hierarchically porous monoliths in polymethylsilsesquioxane sol-gel system.
abstract: A transition from hierarchical pore structures (macro- and meso-pores) to uniform mesopores in monolithic polymethylsilsesquioxane (PMSQ, CH(3)SiO(1.5)) gels has been investigated using a sol-gel system containing surfactant Pluronic F127. The precursor methyltrimethoxysilane (MTMS) undergoes an acid/base two-step reaction, in which hydrolysis and polycondensation proceed in acidic and basic aqueous media, respectively, as a one-pot reaction. Porous morphology is controlled by changing the concentration of F127. Sufficient concentrations of F127 inhibit the occurrence of micrometer-scale phase separation (spinodal decomposition) of hydrophobic PMSQ condensates and lead to well-defined mesoporous transparent aerogels with high specific pore volume as a result of the colloidal network formation in a large amount of solvent. Phase separation regulates well-defined macropores in the micrometer range on decreasing concentrations of F127. In the PMSQ-rich gelling domain formed by phase separation, the PMSQ colloidal network formation forms mesopores, leading to monolithic PMSQ gels with hierarchical macro- and meso-pore structures. Mesopores in these gels do not collapse on evaporative drying owing to the flexible networks and repulsive interactions of methyl groups in PMSQ.
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan. kanamori@kuchem.kyoto-u.ac.jp
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Kanamori
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Kodera
authors.forename: Gen
authors.initials: G
authors.lastname: Hayase
authors.forename: Kazuki
authors.initials: K
authors.lastname: Nakanishi
authors.forename: Teiichi
authors.initials: T
authors.lastname: Hanada